1. Field of the Invention
The present invention relates to an individual identification device which identifies an individual not only by detecting an individual identification number (ID), but also by detecting bodily characteristics of an individual, more specifically, an image of blood vessels of a hand of the individual.
2. Description of the Related Art
As the method of confirming the identity of a person who, for example, enters and leaves a facility without assistance from anyone, there is a method which uses a magnetic card and a PIN (personal identification number). In these methods, however, there is a problem in that, for example, the magnetic card may be lost (forgotten) or plagiarized. As the method of confirming the identity of the person without having any risk of losing (forgetting) or plagiarizing the magnetic card, the method which uses bodily characteristics such as fingerprint and face has been studied.
The verification process of judging whether the user of the card is the individual who is represented by the card or the identification number, and the identification process of judging that the user is one of the specific people who have been registered are carried out according to the difference of bodily characteristics. The verification process and identification process are collectively referred to as individual identification.
Fingerprints, iris, face, blood vessels of a hand, etc. are used as bodily characteristics in individual identification. Instruments for measuring these characteristics are largely classified into a contact type and a noncontact type according to the measurement method. Since the individual identification of an unspecified large number of people needs to be implemented, for example, for the management of people who enter and leave a facility, a noncontact type instrument is more preferable in consideration of the sanitary aspect and psychological resistance of the user.
The bodily characteristic which is best used at present is a fingerprint, but as a finger must be pressed, the measuring instrument is a contact type instrument. As the instrument for measuring the iris, a noncontact type as well as a contact type is available, but there is a problem in that the instrument is expensive and the psychological burden of the user when the iris is imaged is large. The measurement of a user's face can be implemented using an inexpensive noncontact type camera, but it is not possible to make the identification accuracy very high due to the changes of countenance, etc.
The individual identification technology using a hand blood-vessel image was basically disclosed in patent document 1 and patent document 2 described below. Talking of the imaging of blood-vessels of a hand, there is a feature in that the user's psychological burden is small, and the identification accuracy is comparatively high, and that since the hand is imaged with near infrared radiation, the imaging of blood-vessels of a hand is strong against the changes of external light.
Patent document 1: British patent No. 2,156,127
Patent document 2: U.S. Pat. No. 4,699,149
Blood vessels of a hand can be imaged without bringing a hand into contact with the imaging device, but from the viewpoint of improving the identification accuracy, imaging a hand while having the hand fixed on the imaging device is more advantageous. Representative imaging devices commercially available at present are all contact type devices, which image the blood vessels of a user's hand which is brought into contact with part of the imaging device. Disclosed, for example, in patent document 3 below is an invention related to the product made by a Korean manufacturer which images the blood vessels of a hand, the back of which is pressed on the camera thereof. This product is of the type which images the back of one's hand while one holds a pole with one's hand. Disclosed in patent documents 4 and 5 are the inventions related to a product made by a U.S. manufacturer which images the palm of one's hand while one holds a pole with one's hand.
Patent document 3: Kokai (Japan. unexamined patent publication) No. H10-295674
Patent document 4: Kokai No. H11-512203
Patent document 5: U.S. Pat. No. 5,793,881
The individual identification devices using an image of blood-vessels of a hand which are commercially available at present are of the contact type in which a hand must be pressed on the devices, and these contact type devices have a problem in that from the viewpoint of a sanitary aspect and a feeling of cleanliness, the psychological burden of a user is large, and the devices become sticky particularly in summer, so that imaging blood vessels of a hand in a noncontact way is preferable. However, there is a problem in that when blood vessels of a hand are imaged in a noncontact way, it is difficult to obtain good blood-vessel images.
A first problem pertaining to the imaging of blood vessels in a noncontact way is that since blood vessels are imaged without fixing a hand, the opening, position and direction of the hand change each time the blood vessels of the hand are imaged. A second problem is that since, for example, near infrared radiation does not sufficiently cover the blood vessels of the hand, this imaging method is easily affected by external light.
In order to produce a better image of blood vessels, it is preferable to irradiate the surface of the hand skin almost orthogonally with near infrared radiation and also to make the optical axis of the camera orthogonal to the surface of the hand skin. However, there is a third problem in that when blood vessels of a hand are imaged in a noncontact way, the hand, camera and near infrared radiation are not necessarily arrayed in an optimum position, so that the quality of the image is prone to deteriorate.
In view of the above-described problems, the present invention has been developed to realize an individual identification device in which the psychological burden of a user is small and which is sanitary and cleanly by imaging blood vessels of a hand without bringing the hand into contact with the imaging device. It is difficult to obtain a good image of blood vessels under a noncontact condition, but it is the purpose of the present invention to make it possible to obtain a good image of blood vessels under a noncontact condition by contriving the configuration of the imaging device and to realize sufficient identification accuracy by using an identification method suitable for imaging blood vessels in a noncontact way.